This invention is related to the field of compositions that comprise polyolefins that comprise ethylene.
Changes in the density, molecular weight, or molecular weight distribution of a polyolefin that comprises ethylene can noticeably affect its physical properties. For example, the impact strength of an article made from such a polyolefin will decrease, if that article is made using another polyolefin that has either a higher density, a lower molecular weight, or a broader molecular weight distribution, other factors being equal. Conversely, the impact strength of an article made from such a polyolefin will increase, if that article is made using another polyolefin that has either a lower density, a higher molecular weight, or a narrower molecular weight distribution, other factors being equal.
Certain polyolefins that comprise ethylene can be injection molded. These injection-moldable polyolefins typically have melt indices from about 5 to about 100 grams per 10 minutes. An injection-moldable polyolefin that has a melt index lower than another injection-moldable polyolefin, will have a higher impact strength, however, such a polyolefin will be harder to process through an injection-molding apparatus, other factors being equal. Additionally, injection-moldable polyolefins typically have molecular weight distributions from about 2 to about 35. An injection-moldable polyolefin that has a narrower molecular weight distribution than another injection-moldable polyolefin, will have a higher impact strength, however, such a polyolefin will be harder to process through an injection-molding apparatus, other factors being equal.
It has long been desirable to produce polyolefins that comprise ethylene where such polyolefins have better impact strength. This is because less polyolefin would be needed to produce a product that has an impact strength similar to a product made using a polyolefin having a lower impact strength.
It is an object of this invention to provide a polyolefin composition that has an improved impact strength.
It is another object of this invention to provide a process to improve the impact strength of a polyolefin composition.
These and other objects of the invention will become better understood with reference to the following description, examples, and claims.
In accordance with this invention a polyolefin composition is provided that has an improved impact strength. This polyolefin composition comprises (or optionally consists essentially of, or consists of):
(a) a polyolefin that comprises (or optionally consists essentially of, or consists of) ethylene, wherein said polyolefin has a melt index from about 3 to about 10 grams per ten minutes and a density greater than 0.938 grams per cubic centimeter; and
(b) dibenzylidene sorbitol, in an amount equal to, or greater than, the amount required to increase the notched izod impact strength of a composition that consists essentially of said polyolefin and said dibenzylidene sorbitol, by greater than about 10 percent over the notched izod impact strength of a composition that consists essentially of said polyolefin.
In accordance with this invention a polyolefin composition is provided that has an improved impact strength. This polyolefin composition comprises (or optionally consists essentially of, or consists of):
(a) a polyolefin that comprises (or optionally consists essentially of, or consists of) ethylene, wherein said polyolefin has a melt index from about 3 to about 10 grams per ten minutes and a density greater than 0.938 grams per cubic centimeter; and
(b) dibenzylidene sorbitol, in an amount from about 50 to about 50000 parts per million by weight of said polyolefin.
In accordance with this invention a process of using dibenzylidene sorbitol to improve the impact strength of a polyolefin is provided. This process comprises (or optionally consists essentially of, or consists of) contacting:
(a) a polyolefin that comprises (or optionally consists essentially of, or consists of) ethylene, wherein said polyolefin has a melt index from about 3 to about 10 grams per ten minutes and a density greater than 0.938 grams per cubic centimeter; and
(b) dibenzylidene sorbitol, in an amount equal to, or greater than, the amount required to increase the notched izod impact strength of a composition that consists essentially of said polyolefin and said dibenzylidene sorbitol, by greater than about 10 percent over the notched izod impact strength of a composition that consists essentially of said polyolefin.
In accordance with this invention a process of using dibenzylidene sorbitol to improve the impact strength of a polyolefin is provided. This process comprises (or optionally consists essentially of, or consists of) contacting:
(a) a polyolefin that comprises (or optionally consists essentially of, or consists of) ethylene, wherein said polyolefin has a melt index from about 3 to about 10 grams per ten minutes and a density greater than 0.938 grams per cubic centimeter; and
(b) dibenzylidene sorbitol, in an amount from about 50 to about 50000 parts per million by weight of said polyolefin.
In general, the polyolefin compositions of this invention comprise a polyolefin and dibenzylidene sorbitol.
The polyolefins that can be used in this invention comprise ethylene. That is, they can be either homopolymers or copolymers. If the polyolefin used is a copolymer, ethylene should be the major component, as measured by mole percent, of the copolymer. It is preferred if the comonomer in the copolymer is an alpha-olefin having from 3 to 20 carbon atoms in its molecular structure. It is more preferred if the comonomer is selected from the group consisting of propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 3-ethyl-1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and mixtures thereof.
The densities of these polyolefins should be greater than 0.938 grams per cubic centimeter as measured in accordance with ASTM D1505 This is because dibenzylidene sorbitol is not as useful in improving the impact strength of polyolefins that have densities critically lower than 0.938 grams per cubic centimeter. However, It is preferred if the densities of these polyolefins are in the range of about 0.94 to about 0.98 grams per cubic centimeter. This because dibenzylidene sorbitol is more useful in improving the impact strength of polyolefins that have densities in this range.
The melt indices of these polyolefins should be in the range of about 3 to about 10 grams per ten minutes as measured in accordance with ASTM D1238(190/2.16). This is because dibenzylidene sorbitol is not as useful in improving the impact strength of polyolefins that have melt indices critically lower than about 3 or critically higher than about 10 grams per ten minutes. However, it is preferred if the melt indices of these polyolefins are in the range of about 4 to about 9 grams per 10 minutes. This is because dibenzylidene sorbitol is more useful in improving the impact strength of polyolefins that have melt indices in this range.
The molecular weight distribution should be in the range of about 2 to about 8. However, higher and lower molecular weight distributions may be used.
These types of polyolefins can be made by any method know in the art. For example, chromium oxide catalysts, titanium halide catalysts, and transition-metal metallocene catalysts can be used to make these types of polyolefins. All of these catalysts are known in the art and the processes for making these polyolefins using these catalysts are also known in the art.
There are several processes known in the art to make dibenzylidene sorbitol. The structure of dibenzylidene sorbitol is as follows: 
The amount of dibenzylidene sorbitol to contact with a polyolefin, is an amount equal to, or greater than, the amount required to increase the notched izod impact strength of a composition that consists essentially of said polyolefin and said dibenzylidene sorbitol, by greater than about 10 percent over the notched izod impact strength of a composition that consists essentially of said polyolefin. The notched izod impact strengths are measured in accordance with ASTM method D256-90b using injection molded test specimens. However, it is preferred if the amount is equal to, or greater than, the amount required to increase the notched izod impact strength of a composition that consists essentially of said polyolefin and said dibenzylidene sorbitol, by greater than about 30 percent over the notched izod impact strength of a composition that consists essentially of said polyolefin. However, it is even more preferred if the amount is equal to, or greater than, the amount required to increase the notched izod impact strength of a composition that consists essentially of said polyolefin and said dibenzylidene sorbitol, by greater than about 70 percent over the notched izod impact strength of a composition that consists essentially of said polyolefin.
Usually, the amount of dibenzylidene sorbitol to contact with a polyolefin is from about 50 to about 50000 parts per million by weight of said polyolefin. However, in most cases, it is preferred if the amount of dibenzylidene sorbitol contacted with a polyolefin is from about 250 to about 25000 parts per million by weight said polyolefin. Furthermore, it is more preferred if the amount of dibenzylidene sorbitol contacted with a polyolefin is from about 1000 to about 10000 parts per million by weight said polyolefin.
If the amount contacted with a polyolefin is too low, then the impact strength of said polyolefin will not be substantially increased. However, if the amount contacted with a polyolefin is too high, then the other physical properties of said polyolefin may be adversely affected.
Dibenzylidene sorbitol and a polyolefin can be contacted together by any manner known in the art that intimately blends these two components together. For example, a polyolefin and dibenzylidene sorbitol can be combined together and extruded into a suitable form. As an additional example, dibenzylidene sorbitol can be mixed with a suitable carrier and then blended with a polyolefin in any manner known in the art.